The invention relates to a measurement pickup, in particular an electric measurement pickup, for motions of a mechanical part, and to a method for producing it.
In a measurement pickup known from German Patent Disclosure DE 38 27 937 A1, a measurement circuit with a sensor element is disposed on carrier parts and surrounded by a housing. The housing is a caplike connection part, which receives on end of a connection cable. The caplike connection part, which forms a first carrier part, receives a second carrier part, which together with a fourth carrier part receives a third carrier part and is positioned relative to the first carrier part.
The electronic measurement circuit is disposed between the third carrier part and the fourth carrier part in a chamber and is cast with a casting composition. This electronic circuit is connected to a line segment that extends between the second and fourth carrier parts toward the sensor element. In the region of the sensor element, toward the second and fourth carrier part, a further carrier part is disposed, which receives the sensor element. The housing at least partly surrounds the second, third, fourth and one further carrier part and engages the first carrier part, which is embodied as the caplike connection part. To enable to measurement pickup to be disposed in its intended position, a further carrier part is provided, which has a bore for receiving the housing and which carries the measurement pickup therein.
This kind of embodiment of an electric measurement pickup has the disadvantage above all that, as described above, many carrier parts are needed for receiving the measurement circuit and creating an electric connection between the sensor element and the connection cable by means of electric connecting lines. This requires a complicated embodiment of the numerous carrier parts and thus entails high tool costs. Furthermore, assembly is expensive because of the high number of carrier parts. Another factor is that because of the complicated design of the carrier parts and the attendant compulsory order of assembly, there is a high rate of defects in terms of the operability of an electric measurement pickup of this kind.
The measurement pickup of the type defined at the outset is advantageously refined by the characteristics of the invention recited in the main claim, because a simple, compact design is thereby made possible. In a simple way, the sensor element, measurement circuit, contact pins and connecting lines are all mounted on a single carrier part. According to the invention, the carrier part comprises a palladium-filled plastic body, onto which conductor tracks for forming the connecting lines can be applied galvanically at predetermined locations.
In an alternative version of the measurement pickup, the sensor element, measurement circuit and connecting lines are mounted on a first carrier part; the contact pins are mounted on a further carrier part. Once again, the first carrier part comprises a palladium-filled plastic body, onto which conductor tracks for forming the connecting lines can be applied galvanically at predetermined-locations. With this two-piece version of the carrier part, versions of the measurement pickup of different length can be realized in a simple way, since the further carrier part with the contact pins can be mounted separately on the first carrier part. The contact pins in both cases can be applied galvanically by means of a layer of copper or tin, or can be made by a metal inlay part.
To embody the measurement pickup as a phase transducer for detecting the rotary angle in a mechanical arrangement, the sensor element is for instance formed of a magnet cast integrally into or fastened in the carrier part, and with a Hall element as a component of the measurement circuit, any influence on the magnetic field by a rotating part is detected.
The production of the measurement pickup of the invention can in particular be simplified by providing that separate electronic components and/or integrated electronic circuits can be applied directly to the surface of the carrier part for the sensor element. The electrical terminals can especially advantageously be made by reflow soldering or bonding to the locations of the surface of the carrier part that function as conductor tracks.
It is also especially advantageous if the connecting lines, in particular in the longitudinal direction between the sensor element and the contact pins, have corrugations on the surface of the carrier part, to allow longitudinal expansion. As a result, a temperature-related expansion of the carrier part can be compensated for in a simple way.
In an especially advantageous production method, in a first method step in a molded interconnected device (MID) production process, the palladium-filled carrier part is cast by injection molding. In a second method step, a protective plastic coating is sprayed onto those regions of the carrier part where no electrically conductive connections are to be created. In a third method step, the connecting lines are applied galvanically onto the surface of the carrier part, thus forming the conductor tracks.
In a fourth method step, the sensor element and the measurement circuit are applied. For instance, the magnet can be kept spaced apart with ribs and can be mounted positionally fixed in the carrier part. The thus-mounted components can be further covered, adhesively bonded, or hot-calked in the region of the sensor element with a plastic or ceramic lid. Next, in a fifth and final method step the entire arrangement is spray-coated with plastic.